1. Field of the Invention
The present invention relates generally to remote commanders and more particularly to a remote commander of small size which is suitably used for remote control of a television receiver or the like.
2. Description of the Prior Art
Known remote commanders of wireless type are designed to transmit a command signal such as radio waves, ultrasonic waves and infrared rays. Most of the remote commanders now available are designed to transmit a command signal such as a pulsed signal obtained by pulsing infrared rays on and off.
FIG. 1 is a schematic block diagram showing an example of a prior-art digital remote commander utilizing infrared rays as a command signal.
In FIG. 1, a remote commander 1 includes keys 2 such as a power switch, a channel-up key, a channel-down key, a sound volume-up key, and a sound volume-down key for a television receiver and a picture search mode key for a videotape recorder (VTR), etc. When any of these keys 2 is pressed, key data corresponding to the pressed key 2 is generated by a key decoder 3. The key data from the key decoder 3 is supplied to a data encoder 4 that produces a data code 4a. The waveform of the data code 4a is represented in FIG. 2B. The data code 4a from the data encoder 4 is fed to a modulator 5. The modulator 5 is also supplied with a carrier 6a having a frequency from 33 kHz to 40 kHz from a carrier generator 6. The waveform of the carrier 6a is represented in FIG. 2A. The modulator 5 modulates the carrier 6a by the data code 4a and generates a command signal 5a. The command signal 5a is generated at every frame as shown in FIG. 2C. The command signal 5a from the modulator 5 is amplified by an amplifier 7 and is transmitted through a light emitting element 8 such as a light emitting diode (LED) or the like to a controlled apparatus 10, for example, a television receiver or the like, as infrared rays. In FIG. 1, reference numeral 9 designates a power source such as a battery (or dry cell) of size AA of 1.5 V according to the ISO (International Organization of Standards). In this example, the remote commander 1 needs two batteries to drive its respective circuits.
In the controlled apparatus (e.g., television receiver) 10, the infrared rays are received by a light receiving element 11. The light receiving element 11 can be a photodiode or the like. The infrared rays received are then amplified by an amplifier 12, and the amplified signal is amplitude-limited by a limiter 13. The output signal from the limiter 13 is detected by a detector 14 and the data thereof is decoded by a decoder 15. The decoder 15 is directly supplied with data from a key apparatus 16 of the television receiver 10. In response to the data decoded by the decoder 15, a pulse generator 17, a flip-flop circuit 18, a digital-to-analog (D/A) converter 19 or the like are operated to perform the channel-up or -down operation, the switching operation of the switch, the sound volumn-up or -down operation or the like.
Recently, the prior-art remote commander 1 as described above has been designed to decrease its thickness as shown in FIG. 3 and is formed in, for example, a so-called credit card size. As shown in FIG. 3, the light emitting element 8 of the remote commander 1 or the like is made flat, and the battery 9 is a single button-sized lithium cell of a high voltage type of, for example, 3 V.
In the prior art remote commander 1 as described above, the several circuits 3 to 7 provided in the remote commander 1 are fabricated as integrated circuits so that these circuits 3 to 7 can be operated under small power. There is, however, the problem that much greater power is needed to operate the LED of the light emitting element 8 to emit infrared rays. More specifically, a forward voltage drop of the infrared ray emitting diode is about 2 V so that a high voltage battery is needed to cause a light emitting current to flow. Further, a voltage of at least about 3 V is needed to drive the integrated circuit for transmitting a remote control signal so that two ordinary batteries of size AA of 1.5 V are generally required. While the credit-card type remote commander 1 shown in FIG. 3 needs one battery, the battery used therein is a special high voltage type producing an output voltage of 3 V and formed as a button type. Thus, the prior-art remote commander 1 unavoidably needs a special high voltage battery.